1. Field of the Disclosure
The present disclosure relates to a directional coupler, and more particularly, to a directional coupler including a main line and a sub line electromagnetically coupled with each other.
2. Description of the Related Art
As an example of directional couplers of the related art, the directional coupler disclosed in Japanese Patent No. 3203253 is known. This directional coupler includes first and second coupling lines formed in a spiral shape. The first and second coupling lines are superposed on each other in the vertical (top-bottom) direction and are electromagnetically coupled with each other. With this configuration, the first coupling line serves as a main line, while the second coupling line serves as a sub line.
In the directional coupler disclosed in this publication, there may be a case in which adjustment is desirably made so as to reduce the degree of coupling between the first coupling line (main line) and the second coupling line (sub line). This can be realized by increasing the vertical distance between the first and second coupling lines. This, however, increases the height of the directional coupler. Thus, in the directional coupler disclosed in this publication, it is difficult to reduce the degree of coupling between the main line and the sub line while implementing a decreased thickness of the directional coupler.